light.lua

local mon = peripheral.find "monitor"
local wasCol = colors.green

while true do
    local r = math.random()
    local col = nil

    if wasCol == colors.red then
        col = colors.orange
    elseif wasCol == colors.orange then
        if r >= 0.5 then
            col = colors.green
        else
            col = colors.red
        end
    elseif wasCol == colors.green then
        col = colors.red
    end

    mon.setBackgroundColor(col)
    mon.clear()

    wasCol = col

    sleep(3)
end